Radio station center tuning control



March 21, 1939. A. LESTl ,1

RADIO STATION CENTER TUNING CONTROL Filed April 1'7, 1937 4 Sheets-Sheetl INVENTOR March 21, 1939. A. LESTI RADIO STATION. CENTER TUNING CONTROLFiled April 1'7, 1937 4 Sheets-Sheet 2 March 21, 1939. A E 2,151,275

RADIO STATION CENTER TUNING CONTROL Filed April 17, 1957 4 Sheets-Sheet5 F'IGJ INVENTOR March 21, 1939. A -r 2,151,275

RADIO STATION CENTER TUNING CONTROL Filed April 17, 1957 4 Sheets-Sheet4 INVENTOR Patented Mar. 21, 1939 UNITED STATES BATENT FFEQE RADIOSTATION CENTER TUNING CONTROL Arnold Lesti, Los Angeles, Calif.

Application April 17, 1937, Serial No. 137,509

13 Claims.

My invention is in a radio tuning control to permit accurate tuning ofradio receivers to radio transmitting stations and to render inaccuratetuning impossible. My invention also constitutes a radio stationindicator to give a visible indication of radio stations that aretransmitting.

An object of my invention is to provide radio receivers with a tuningcontrol whereby radio stations are not heard in the loud speaker unlessthe tuning is in the proper point of resonance.

In radio reception a station will not be received properly when detuned.

Another object of my invention is to provide a light signal when thereceiver to which my invention is applied, is accurately tuned to thecenter of the frequency band which constitute the radio signal, whilesimultaneously the audible tones or modulations of the station are heardin the loud speaker. In radio reception there is a considerable rangeover which the carrier frequency gives equal response and it isdifficult to determine where the proper center of response should be.When the response curve has several peaks or is substantially flat overa wide range tuning meters or indicators give the same readings forvarious positions of the tuning control and thus accurate tuning isdiflicult.

In the construction of my invention I have found that shutters may beutilized to represent a range of frequencies from corresponding detunedportions on both sides of the exact tuning point of a signal and thatthe center of these shutters automatically may switch an electricalcircuit to control the above mentioned loud speaker or lamp when alltuned circuits are in perfect alignment.

An important feature of my invention is that it provides interstationnoise suppression between substantially accurate and very narrow pointsof resonance of radio stations received.

Another detailed object of my invention is to provide a simultaneousvisible indication of all radio transmitting stations within thereceptive range of any radio receiver to which my novel .3 invention isapplied and to provide such indication while the radio receiver is use-din its normal function and also to utilize the apparatus alreadyinherent in the receiver to obtain the above objects.

I have found that while a radio receiver may be in tune with only onestation at a time, it is possible to utilize a series of shutters togive a simultaneous indication of many radio stations. Each shutter mayoperate separately and independently as the tuning element of thereceiver is varied and the full sweep of the tuning element will bringeach individual shutter in succession into operative influence. As theproper shutters are operated I found that they may be held operated evenafter the operating influence has passed.

A further detailed feature is to provide an adequate, simple andinexpensive indicator of the above type in which the shutters are selfrestoring whenever certain stations may cease transmitting or if thewave band to which the receiver is receptive may be changed; the effectis brought about whenever the tuning element is again varied throughoutits entire range.

Another object of my invention is to eliminate the crowding of stationson the low wavelength side of the dial and to provide substantially anevenly calibrated dial on conventional radio receivers. It is well knownthat conventional radio receivers do not have straight line frequencyresponse of the tuning control; 1. e., the rate of change of frequencywith respect toangular movement of the tuning control is not a constant.As a result there is a crowding of stations on the low wavelength sideof the tuning range.

While I have. shown my invention as applied to radio reception it shouldnot be considered as being so limited. It may be used generally forelectrical control and indication.

With the foregoing and other objects and features in view which will bemade manifest in the following detailed description and pointed out inthe claims, reference is had to the accompanying drawings for anillustrative embodiment of the invention wherein:

Fig. 1 is a front view of the indicator with the escutcheon andattachments removed.

Fig. 2 is a sectional View on the line 2-2 of Fig. 1, showing also theescutcheon and attachments in section and the relay.

Fig. 3 is a view of the line 33 of Fig. e with the relay removed showingthe centering feeler assembly.

Fig. 4 is an enlarged view on the line 2-4 of Fig. 1 showing thecentering feeler and feeler lift assembly. The shutters are shown on theline [5-45 of Fig. 1.

Fig. 5 is a view of the feelers and shutters when the relay isenergized.

Fig. 6 is a view illustrating the action of the feelers when detuned tothe right.

Fig. 7 is a View illustrating the action of the feelers when detuned tothe left.

Fig. 8 is a view illustrating the action of the feelers at perfectcenter tuning.

Fig. 9 is a view of the elliptical gears on line 9-9 of Fig. 2.

Fig. 10 is a perspective view of part of the shutters and feelers.

Fig. 11 is a View on the line |l|| of Fig. 4.

Fig. 12 is a front reduced view of the indicator.

Fig. 13 is a view of part of the movable slotted disc with feelersthereon.

Fig. 14 is a diagrammatic View of a conventional radio receiving circuitof a general type showing a method of applying the invention thereto.

Referring to the accompanying drawings wherein similar parts arerepresented by similar numbers throughout, l6 represents the movablerelay which is rotatable when the variable tuning element of the radioreceiver is moved. This tuning element is usually a series of gangedvariable condensers. The shaft of these condensers ll connects to theshaft i9 by universal joint coupling I9. The movable relay I6 isrotatable with shaft 2| and the disc 22 is held by screws not shown tothe base of the relay H5. The entire relay and its assembly movesthrough substantially 180 degrees as the tuning element is turnedthroughout its entire range. Armature 23 is hinged by pivot screws 24,25, and finger 29 is held to the back face of the armature. When therelay coil 27 is energized the armature will be moved towards the core29 and the finger 29 will move several shutters 29 inwards towards therotatable disc 22. Only one shutter will be moved through the slot 39.As the disc moves the shutters that have been moved through the slot 39will remain on the back face 3| of the disc. If the relay is energizedand the shaft rotated all shutters will be moved through the slot andheld by the back face 3| of the disc 22. If the armature 23 is restoredto normal every shutter will also be restored to normal as rotationtakes place ex cept where the armature may be held operated. As a resultof discontinuous operations of the armature a series of shutters may bemoved towards the back face of disc 22 while others may remain adjacentto the front face 32. The result of this procedure is an appearance suchas is shown generally by 33 in Fig. 1. I prefer to energize the relay asdescribed below, when the radio receiver is detuned, in which case theseries of shutters held normally adjacent to the front face 32 willconstitute an indication of radio stations received as the tuningelement of the receiver is varied. The front face 32 of the disc 22 isof a finish to provide contrast with the shutters 29 which may be eitherblack, dark blue or any other suitable shade.

The position of the shutters adjacent the front face 32 may beconsidered their operated position, in the preferable form of theinvention, and after going through the slot, while held on the back face3!, they may be considered as being in their normal position. However,in the alternative method of indicating the stations received, whereinblank spaces adjacent the front face 32 may correspond to the stationsreceived, the opposite nomenclature may be used, i, e., adjacent thefront face 32 the shutters may be considered as being in their normalposition, while in the back face they may be considered as being in theoperated position. Knobs 34 and 35 are turned during the tuningoperation. I prefer a planetary reduction box 39 of conventional designto give the knob 34 high speed and 35 low speed. These knobs turn pulley3'! to move friction belt 38 which turns pulley 39. This pulley isintegral with gear 40 which engages gear 4! fastened to pinion 42 todrive gear 43 fixed to the shaft 2| by a set screw. This arrangementgives a large reduction in speed to turn the relay I6 and its assembly,together with the disc 22 and its assembly. Other suitable arrangementsmay be used. The elliptical gear 44 also turns integrally with shaft 2|as does likewise pointer 46 to show the particular shutters or tuning towhich the radio instrument is set. The elliptical gear 44 is coupled toits mate by springs 41, 48 and both gears engage elliptical gear 49. Thearrangements of the three gears 44, 45 and 49 permits coupling betweenshafts l8 and 2| without back-lash.

In order to allow each shutter to cover the same frequency change in allparts of the dial and also to eliminate the defect of crowding, theelliptical gears are used to provide a stepup ratio between shafts l8and 2| whereby 2| travels faster than l8 at the low wave length settingsof the variable tuning element of the receiver and 2| travels slowerthan l8 at the high wave length settings, The efiect is made sufficientto obtain substantially a constant for the rate of change of frequencywith respect to angular movements. This system is preferable, but if theradio has straight line frequency response it may be eliminated, inwhich case 2! is directly coupled to H. The universal joint coupling I9is used to relieve the load on elliptical gear springs 41, 48 if shaft18 is placed slightly out of alignment with H.

The opening 59 permits light from the lamps 5| to provide indirectillumination. I prefer a convex transparent glass 52 held by snap ring53 on the escutcheon 54 as shown to cover the scale 55 and pointer 46.

While I have shown the shutters 29 in a preferably semicircular form,this arrangement is not absolutely necessary. may extend in a completecircle or, where space is ample, the shutters may extend substantiallyin a straight line. In this latter case the movable relay would move ina straight line. The shutters 29 are preferably made from very thinsheet steel with clearances or openings 59. Each shutter has a free end5.! and wide end 58 to give strength. I have shown only 138 shutters inFig. 1 in order to illustrate detail but actually a large number isnecessary. I have used 380 shutters for radio receivers to cover a rangeof about one megacycle for a complete sweep of the tuning control, WhileI have shown my invention in a preferable form it should not beconsidered as being so limited as various obvious changes may be made bythose skilled in the art without departing from the broad aspect of thisinvention.

When the shutters are moved by the finger 26 the free end 51 moves in adirection perpendicular to the plane of the material from which theshutters are made towards the slot 30, referring to Fig. 5, to the rear59 of the disc 22. Referring to Fig. 3 the feelers 69 and GI are rivetedto disc 22 at 62 and bear down towards the shutters 29 at the slot 30.These feelers move independently by spring action and have tapered edges63 and 54, as shown in. Fig. 4, and the center between the feelers 65coincides with the slot 39. The feeler springs 66 and 61 make In somecases they.

A closed circuit may be traced from lead 13 to springs I5 and I39 tofeeler spring 66, to feeler spring tip I I, to feeler 60 and to feeler6|, feeler spring tip I2 and feeler spring 61 to 14. This circuit may beopened as illustrated in Figs.

5, 6 and 7.

Link I8 is fixed to 26 and movable with the armature. There is a hole inthe link to receive pin I9 held to piece 80 pivoted by} pivot screws 82,82 so that any movement of the armature is linked to 80 causing a smallrotation of this member. Feeler lift BI is fixed to 80 and provides amagnified movement to lift the feelers when the armature is operated asshown in Fig. 5 and thereby allow the shutters to move freely throughthe slot. When the armature is restored the feeler lift releases thefeelers which exerts pressure on any shutter which may be present in theback face 3|. This aids the normal self restoring springing action ofthe shutters and insures positive and complete restoration.

As explained below, radio stations give an indication such as 83, 84 and85, Fig. 6. The width of these indications is related to the strength ofthe station to which they correspond. In Fig. 10 is shown how thefeelers 60, 6| engage the operated shutters in the back face of the disc22. The slot opening 89 allows a free movement of the feelers. For awide indication the feelers will move by spring action towards the frontface 32 to a greater degree than for a smaller indication. In Fig. 6,when a station is detuned to the right, feeler BI is raised higher than60 by the end of a shutter. This moves the entire spring assembly tobreak contact at 60 to 'II. In Fig. '7, when a station is detuned to theleft feeler 60 is raised higher than 6I by the end of the shutter whichcorresponds to a detuned portion of the radio station, similarly to thedetuned portion on the other side of the exact center 81 which causedthe raising of feeler 6I. Feeler 60 may thus cause a breaking betweencontact at BI and I2. The breaking or the opening of the circuit ofleads I3 and I4 silences the radio speaker and turns off a lamp asmentioned above and as is explained in detail below. Fig. 8 illustrateshow exact tuning is achieved when both feelers are raised by a similaramount and both make contact with the feeler spring tips II and I2 toclose the circuit of leads I3 and I4. I prefer to render the loudspeaker operative at this time and to light a lamp to indicate exactresonance. Line 88 indicates the amount of detuning of the entiremovable assembly and tuning system with respect to the position of exacttuning of station 84 represented by the dotted line 87. I prefer toprovide an insulating washer 20 of the universal joint I9 to insulatethe shaft I8 from the chassis of the radio to which this device isapplied. The frame H8 should also be insulated from the chassis when itis fixed thereon. Referring to Fig. 14 radio frequency currents presentin the antenna I to ground are coupled to the imput grid of tube 89 andtuned by variable condenser IN. The amplified currents are transformedfrom the plate circuit of tube 89 to the imput of the mixer tube 90 andtuned by the variable condenser I02. The variable condenser I03 tunesthe local oscillator circuit with tube 95 and this oscillator frequencyis fed into mixer tube 90. The heterodyned output of tube 90 is fed toan intermediate amplifier having tubes 9I and 92. The output of theintermediate amplifier is rectified by tube 93 and demodulated currentsappear across I04 to ground. These currents are fed to the audiofrequency tube 94 the amplified output of which at I05, I06 may beconnected to an audio frequency amplifier not shown. The amplifier issupplied by a source of plate current connecting positive to lead I01and negative from I08. Leads I09 and H0 furnish tube heater currents andalso serve for lighting the indicator lamps I.

Variable condensers IOI, I02 and I03 are ganged together and theircommon shaft is N, Fig. 2. In the tuning operation the radio receivingcircuit will amplify any radio station with which it may be in tune andplace a negative potential due to the carrier frequency, at pointI04,the magnitude of which is proportional to the intensity of thereceived signal. This negative potential is fed to the grid of the tube96 through the battery or source of potential I32. When no signals arepresent switches I3I and I09 are adjusted to cause the tube to passcurrent to energize coil 21. When signals are present and a negativepotential is placed at I04 tube 96 cuts off and no current flows throughcoil 21. Adjustment of switches I3I and I09 will give accurate controlso that signals above a specified minimum will cause tube 96 to sharplycut off. As the shaft I1 is turned during the tuning operation and theentire tuning range is covered certain shutters will be moved throughthe slot 30 to the back face 3| leading a series of shutters in theirnormal position to give a visible indication of stations that are on theair. I prefer to indicate stations as normal unmoved shutters instead ofthe alternative of moving the shutters to indicate stations, as there isno current flowing through coil 21 when the re-' ceiver is tuned to astation in the system which I disclose in Fig. 14. The center tuningfeature may be eliminated by grounding lead I4.

In Fig. 14 lead I3 is shown grounded and lead I4 is connected to thegrid of the audio amplifier tube 94. If spring assembly I I3 and thefeelers and feeler springs all make contact, tube grid return lead H4 isgrounded and amplification of currents from II5 takes place. However, ifthe circuit is broken, as mentioned above in connection with Figures 5,6, and '7, then a high negative potential from lead I08 will charge thegrid of tube 94 and cut off its plate circuit to stop amplification ofaudio currents and silence the loud speaker. I prefer a neon lamp 98 tofurnish light when the tube 94 is amplifying and to darken when thistube is cut off. Since the grid is practically an open circuitresistance II2 may be very high and I have found that five megohms maybe used to reduce to a very low value the current that fiows through thefeeler contacts, in order to prevent arcing and insure long life. Ifmore light is required than can be furnished by lamp 98, a separate tube91 may be used with a powerful lamp 99. Leads H6 and III are thenconnected together. The procedure to obtain center tuning is to firstsweep the dial and then turn to any station desired as indicated by thepointer 46. When the exact center is reached the neon lamp 98 will lightand the loud speaker of the radio will simultaneously translate thedemodulated and amplified audio currents into sound.

Various changes may be made by those skilled in the art in detail ofconstruction of my invention without departing from. the spirit thereofas set forth in the drawings, specifications and claims.

I claim:

1. A radio dial comprising in combination, a series of shutters, amovable member having a slot adapted to allow the passage of theshutters, a radio tuner coupled to said movable member and meansresponsive to a tuned-in signal to move any of the said shutters throughthe said slot to indicate the signals received by the said tuner.

2. A radio station indicator comprising in combination a series ofshutters each having a normal and an operated position, .a radio tuner,a movable member coupled to the said tuner and having a slot adapted toallow the passage of substantially one shutter, means responsive: to atuned-in signal to move any of the shutters through the said slotcorresponding to the settings of the tuner and means to hold theoperated shutters from returning to their normal position.

3. A radio station indicator comprising in combination, a series ofshutters, a radio receiver having a tuner, a movable electro-magnetcoupled to the said tuner and having means cooperating therewith to moveany of the said shutters, when operated, corresponding to stationsreceived by the said tuner, and means for holding any of the said movedshutters from returning to their normal positions whereby a simultaneousindication of shutters is attained corresponding to radio stationsreceived.

4. A radio stations indicator comprising in combination, a series ofshutters arranged sub- .stantially in a circular form and forming aportion of a disc with each shutter having a free end close to thecenter .of the disc and edges that are substantially radii of the discand a fixed end close to the periphery of the disc, a movable memberadapted to be energized and move any of the said shutters and means forholding the moved shutters from returning to their normal positionswhereby a series of shutters is held, corresponding to the energizedpositon of the movable member.

5. A radio station indicator comprising-in combination, a series ofshutter-s, a movable member having a slot to pass substantially oneshutter at a time and. a front face adjacent to the shutters, a backface on the movable member to hold any moved shutter, a relay held tothe movable member and movable therewith, a radio receiver having a loudspeaker, meansfor energizing the relay when the said receiverisdetunedfrom signals, an armature adapted ,to move anyshutters throughthe said slot to the back'face of themovable member when the relay isenergized, a centering switch engaging the moved shutters with meanscooperating therewith tosilence the loud speaker 'for'detuned settingsofthe said receiver.

6. .A radio station indicator.comprising-in combination, aseries ofshutters, a movablemember :having a slot adapted to allow the passage ofsubstantially one shutter at.atime,.a radio am- .plifier andtuner-having a variable element linked and tuner having a variabletuning element coupied to the said movable member, a relay held to themovable member and having an armature with means cooperating therewithto move any shutter through the said slot when the relay is energized,an automatic volume control in the said amplifier to furnish potentialproportional to the received signals, a radio tube with meanscooperating therewith to energize the relay by the automatic volumecontrol potential when signals are detuned whereby shutters are held intheir normal positions corresponding to radio signals received.

8. A radio stations centering switch comprising in combination, twofeeler members each having a tapered edge and movable independently, amovable member engaging each feeler member and means for disengaging onefeeler member from the movable member by the movement of the otherfeeler member.

9. A'radio stations centering switch for spaced protuberances,comprising in combination, two feeler members each having a tapered edgeand adapted to move independently when passed over for placing a seriesof shutters on the back face of the movable member to indicate the radiostation received by the said receiver, two feeler members movableindependently and having tapered edges engaging the shutters on the.back face of the movable member,-means for utilizing the said feelermembers to switch .an electrical circuit when the center position ofspaced shutters is attained corresponding to resonance of the radiostation tuned.

11. A centering SWitCh'fOI radio receivers comprising in combinationaseries of shutters having movable .ends,,a movable member having a slotto pass any of the said shutters, a back face on the said movable memberto hold the moved shutters, a relay integral with the said movablemember and having an armature adapted tomove substantially one shutterthrough the said slot when energized, two feeler springs on the back.face of the movable member having tapered edges engaging the movedshutters, a contact member engaging the said feelers, and means forswitchinganelectrical circuit by the action of thefeelersand the contactmember when the slot on the m va le mem er coincid s w th h ente of aseries f sh tte s eld i th i n rma pet tions- 12. The method ofswitching an electrical circuit when obtaining substantially exacttuning of a radio signal with shutters which consists, in utilizingspaced shutters to correspond to specifled detuned portions on bothsides of the point of exact resonance of a radio signal and utilizingthe center between these shutters to switch the electrical circuitcorresponding to exact tuning.

13. The method of visibly indicating radio signals and electricallyswitching at exact tuning by shutters which consists, in utilizing aseries of shutters to cover a range from specified detuned portions oneach side of the position of exact tuning to give a visible indicationand utilizing the center of the series of shutters for switching atexact tuning.

ARNOLD LES'I'I.

